I. Field of the Invention
This invention relates to molten metal containment structures used for conveying, treating or holding molten metals, particularly such structures incorporating refractory or ceramic molten metal-containing vessels made from or including two or more pieces or sections. More particularly, the invention relates to methods of providing sealed joints between such pieces or sections to prevent leakage of molten metals from the vessels at the joints.
II. Background Art
Molten metal containment vessels, e.g. metal-conveying troughs and launders, are often employed during metal treatment or casting operations and the like, for example to convey molten metal from one location, such as a metal melting furnace, to another location, such as a casting mold or casting table. In other operations, such vessels are used for metal treatments, such as metal filtering, metal degassing or metal transportation. Vessels of this kind are often constructed from two or more shaped sections made of refractory and/or ceramic materials that are resistant to high temperatures and to degradation by the molten metals intended to be contained therein. The vessel sections are brought into close mutual contact and may be held within an outer metal casing or the like provided for support, proper alignment and protection against damage. Sometimes, such vessels are provided with sources of heat to ensure that the molten metals do not cool unduly or solidify as they are held within the vessels. The sources of heat may be electrical heating elements positioned above or beneath the vessels or enclosures for conveying hot fluids (e.g. combustion gases) along the inner or outer surfaces of the vessels.
It is of course important to ensure that molten metal does not leak out of the vessels at the interface between two abutting sections, whether the vessels are heated or not. However, it is especially important to avoid metal leakage when sources of heat for the vessel are provided because the molten metal may cause catastrophic damage to electrical heating elements or other heating means. It is therefore usual to provide a sealed joint between adjacent vessel sections, e.g. by providing a layer of refractory paper between the adjacent sections to accommodate thermal expansion or contraction. A refractory sealant may also be forced into the gap between abutting surfaces of adjacent sections. It is also known to provide sections with a surface groove spanning the abutting sections and to fill the groove with a refractory rope covered with a moldable refractory sealant to fill the joint and to form a smooth interconnecting surface between the vessel sections. However, all such joints deteriorate with time and use due to thermal cycling, especially when used in heated vessels, and the joints eventually allow a direct leak path to appear between the vessel sections.
There is therefore a need for further ways of providing sealed joints for metal-holding and metal-containment vessels.